1. Field of the Invention
The present invention relates to a method of defect review, and more particularly, to a method of defect review using different sampling ratios according to defect types.
2. Description of the Prior Art
In the semiconductor fabricating process, some small particles and defects are unavoidable. As the size of devices shrinks and the integration of circuits increases gradually, those small particles or defects affect the property of the integrated circuits more seriously. For improving the reliability of semiconductor devices, a plurality of tests are performed continuously to find the root cause of the defects or particles. Then, process parameters can be tuned correspondingly to reduce a presence of defects or particles so as to improve the yield and reliability of the semiconductor fabricating process.
Please refer to FIG. 1, which is a schematic diagram of a method of defect detection 10 according to the prior art. As shown in FIG. 1, a sampling 12 is first performed to select a semiconductor wafer as a sample for following defect detection and analysis in advance. Then, a defect inspection 14 is performed. Normally, a proper defect inspection machine is utilized to scan in a large scale to detect all defects on the semiconductor wafer. Since there are too many defects on a semiconductor wafer, a manual defect review with the SEM cannot be directly performed for all defects in practice. A manual defect classification 16 is typically performed before the defect review 18. After separating the defects into different defect types, some defects are sampled for the defect review 18. Then, a defect root cause analysis may be performed in advance according to the result of the defect review 18 to attempt to reduce the defect generation.
In the prior art technology, there is a serious problem of selecting samples. Typically, there are thousands of defects found in the defect inspection 14. However, engineers can only pick a part of them, such as 50 to 100 defects, to perform the defect review 18 and the following defect analysis. The defect sample selection is totally dependent on the personal experience of the engineers. In other words, only a few skilled engineers can pick up some outstanding defects to perform following analysis works by their own experiences. Most operators can only pick up samples randomly for the defect review 18. However, among all defects, most of them are the underlayer defects, which are not related with the current fabricating processes, or some non-killer defects, which have no influence on the yield of fabricating processes. The killer defects, which have a large influence on the yield of fabricating processes, are relatively fewer. Thus, in most cases, since the samples in the defect review 18 are picked up randomly, it is obvious that only a few effective samples are valid and most parts of the defect review 18 are meaningless. This leads to a huge waste of time and effort, deteriorating the accuracy of the following defect analysis.
In the prior art technology, the only way for increasing the accuracy of the defect analysis is by increasing the numbers of samples in the defect review 18 significantly. In other words, a heavy loading and a significantly additional time are unavoidable, leading to a testing time delay and even a serious throughput reduction during the mass production.
With the progression of the semiconductor technology, the size of wafers increases from 8 inches to 12 inches and the line width reduces from 0.18 μm to 0.13 μm and even below 0.1 μm. In the process from testing into the mass production, defects occur very often and are unavoidable. In other words, the defect detection and analysis become more and more important. Thus, a quick and efficient method of defect review is strongly needed to solve the aforementioned problems.